CN109241690B - CFD-based sluice over-current flow calculation method - Google Patents
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Abstract
A water gate over-current flow calculation method based on CFD belongs to the field of hydraulic engineering and comprises the following steps: establishing a geometric model of a sluice calculation domain; (B) meshing; (C) CFD calculation settings; and (D) judging whether the flow set by the C meets the convergence requirement or not. The invention carries out two-phase flow calculation of the upstream and downstream flow fields of the sluice based on ANSYS CFX software, determines the flow by taking liquid phase volume fraction as a criterion, solves the problem of insufficient accuracy of the overflowing flow of the sluice calculated by an empirical formula, and finds that the error of the empirical formula is 15.5 percent after comparing the result with the measured data, but the error can be controlled to be 4.2 percent by the calculation method of the invention, thereby being beneficial to scientific, safe, economic and reasonable design and operation of the sluice.
Description
Technical Field
The invention belongs to the field of hydraulic engineering, relates to a sluice over-current flow calculation method, and particularly relates to a sluice over-current flow calculation method based on CFD software.
Background
The outflow of water controlled by the gate through the opening between the bottom edge of the gate and the gate floor is referred to as the gate bore outflow. In the design of the gate, calculation and check are often required according to the flow rate of overflowing. In addition, when the gate has a fault, the overflow flow of the gate also becomes one of the key parameters for guiding the maintenance and checking the strength of the gate. However, the current flow rate is generally calculated according to an empirical formula, and a situation with a large deviation from an actual situation often occurs in engineering practice. Therefore, a calculation method capable of reliably calculating the overflow flow of the water gate is needed to be researched, and more reliable guidance is provided for engineering practice.
Disclosure of Invention
The invention aims to provide a CFD-based sluice overflow flow calculation method to improve the overflow flow calculation accuracy, aiming at the defects that the overflow flow is generally calculated according to an empirical formula at present, the deviation from the actual condition is large, the sluice overflow flow calculation accuracy is insufficient and the like in engineering practice.
The technical scheme of the invention is as follows: a method for calculating the overflowing flow of a water gate based on CFD is characterized by comprising the following steps:
(A) Establishing a geometric model of a sluice calculation domain;
(B) Grid division;
(C) CFD calculation setting;
(D) And judging whether the flow set by the C meets the convergence requirement or not.
The method for establishing the geometric model of the sluice computational domain in the step (A) comprises the following steps:
(1) According to the geometric parameters of the sluice, three-dimensional modeling software is adopted to establish a three-dimensional geometric model of the sluice;
(2) Taking the position of the gate as a reference, and taking an appropriate value for the distance from the upstream water flow inlet and the downstream outlet to the gate to obtain a three-dimensional model of a flow channel including the water gate, wherein the three-dimensional model is a calculation domain of the water;
(3) The water level of the upstream and downstream is properly extended in the height direction, which is the calculation area of the air.
The mesh division method described in step (B) is as follows:
(1) Exporting the calculation domain established in the step (A) to ICEM CFD, and carrying out grid division on the calculation domain;
(2) Setting proper grid parameters to ensure that the grid is encrypted near a water gate;
(3) Meanwhile, in order to capture the interface between water and air, the grids near the water surface also need to be encrypted;
(4) The total number of grid cells should be controlled to be above a certain number, so as to ensure the reliability of calculation.
The CFD calculation setting method described in step (C) is as follows:
(1) Importing the grid divided in the step (B) into CFD software ANSYS CFX for setting;
(2) The calculation model and the calculation method are as follows: performing flow calculation based on a Reynolds time-mean N-S equation, capturing the change of the water surface by adopting a standard free surface model under a homogeneous phase flow model, and dispersing each item in the time-mean N-S equation by adopting a High Resolution format through adopting a standard k-epsilon model and a turbulent flow model;
(3) Setting a boundary condition: the water area inlet adopts a flow inlet condition, the volume fraction of water is set to be 1, and the volume fraction of air is set to be; the outlet condition is a flow outlet condition, and the flow is estimated according to the following formula:
in the formula, σ s Mu is a coefficient of flooding 0 The flow coefficient of the free outflow of the gate hole, e is the opening height of the gate, b is the net width of each hole, H 0 The water head is a gate front water head comprising a near flow velocity water head, and g is gravity acceleration; the plane where the center line in the width direction of the panel is located is set as a symmetrical plane; the upper surface of the air domain adopts an Opening boundary, the pressure is set to be 0, the volume fraction of water is 0, and the volume fraction of air is 1; the interface between the air area and the water area adopts Gerneral Connection; the other boundaries are set as non-slip wall surfaces;
(4) Setting initial conditions: the volume fraction of water in the air domain is set to 0, and the volume fraction of air is 1; each component of velocity and pressure is set to 0; the volume fraction of water in the water area is set to be 1, and the volume fraction of air is 0; both the speed and pressure are set to 0.
The condition for judging whether the flow rate set by the step (C) meets the convergence requirement is as follows:
(1) Averaging the volume fractions of water on the symmetric surface of water area and air area ave1 And alpha ave2 As a criterion;
(2) If α is ave1 > 0.95 and alpha ave2 If the flow rate is less than 0.18, the flow rate meets the convergence requirement;
(3) If α is ave1 If the flow rate is less than 0.95, the flow rate is low, and the flow rate is adjusted to the original 0.95/alpha ave1 Doubling;
(4) If α is ave1 > 0.95 and alpha ave2 If the flow rate is more than 0.18, the flow rate is higher, and the flow rate is adjusted to be 0.95/alpha of the original flow rate ave1 And (D) repeating steps (C) and (D) until condition (1) is satisfied.
The invention has the beneficial effects that: the invention provides a CFD-based sluice over-current flow calculation method, which is characterized in that two-phase flow calculation of upstream and downstream flow fields of a sluice is carried out based on ANSYS CFX software, the flow is determined by taking liquid-phase volume fraction as a criterion, the problem of insufficient precision of the sluice over-current flow calculated by an empirical formula is solved, the error of the empirical formula is 15.5% after the result is compared with measured data, and the error can be controlled to be 4.2% by the calculation method.
Drawings
Fig. 1 is a flowchart of a method for calculating an overflow flow of a water gate based on CFD according to the present invention.
FIG. 2 is a three-dimensional model of a pump gate according to an embodiment of the present invention.
Fig. 3 is a mesh divided in an embodiment of the present invention.
FIG. 4 is a diagram illustrating boundary condition setting according to an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples:
in the embodiment, a certain domestic pump gate is taken as a research object, the width of the pump gate is 10.2m, the height of the pump gate is 4.5m, the upstream water depth is 5.01m, the downstream water depth is 0.83m, the gate is 1.5m high, and the thickness of a water gate steel plate is 0.01m.
As shown in fig. 1, which is a flowchart of a method for calculating an overflow flow of a CFD-based sluice according to this embodiment, the specific implementation steps are as follows:
(A) And establishing a geometric model of the sluice computational domain.
According to the water gate parameters, a pump gate geometric model is established by adopting three-dimensional modeling software, and as shown in fig. 2, the pump gate geometric model is established in the embodiment of the invention. According to the hydraulic design parameters of the gate station, the upstream is extended to 10.2m, the downstream is extended to 20.4m, the height of the upstream water surface is 5.01m, and the height of the downstream water surface is 0.83m by taking the width of the gate as a reference. The height of the gate from the bottom plate is 1.5m, and a water area is finally obtained. The upstream water surface was 0.5m in height and the downstream water surface was 0.83m in height, which is an air space, with respect to the water area.
(B) And (5) grid division.
Exporting the calculation domain established in the step (A) to ICEM CFD, setting unstructured grid Parameters by adopting Global Mesh Parameters, setting Max element to be 1m and setting Min Size limit to be 0.01m for a water area; for the air domain, max element is set to 0.5m, min Size limit is set to 0.01m. And encrypting the grid near the water surface by using a Prism Mesh, wherein 5 layers of Prism grids are used in total. As shown in fig. 3, the total number of grid cells is 837.5 ten thousand for the grid divided in the embodiment of the present invention.
(C) CFD calculation settings.
And (4) importing the grid divided in the step (B) into CFD software ANSYS CFX for setting.
(1) The calculation model and the calculation method are as follows: performing flow calculation based on a Reynolds time-mean N-S equation, capturing the change of the water surface by adopting a standard free surface model under a homogeneous phase flow model, and dispersing each item in the time-mean N-S equation by adopting a High Resolution format through adopting a standard k-epsilon model and a turbulent flow model;
(2) Boundary conditions are as follows: the water area inlet adopts a flow inlet condition, the volume fraction of water is set to be 1, and the volume fraction of air is set to be; the outlet conditions are also flow outlet conditions, and flow estimation is performed according to the formula (1), wherein sigma s ＝1，e＝1.5m，b＝10.2m，H＝5.01m，μ 0 H is replaced by H because the near flow velocity is generally small =0.6-0.18e/H 0 ，g＝9.81m 2 Q =41.42m by substituting equation (1) 3 S; the plane where the center line in the width direction of the panel is located is set as a symmetrical plane; the upper surface of the air domain adopts an Opening boundary, the pressure is set to be 0, the volume fraction of water is 0, and the volume fraction of air is 1; the interface between the air area and the water area adopts Gerneral Connection; the rest boundaries are set as non-slip wall surfaces (wall);
(3) Initial conditions: the volume fraction of water in the air domain is set to 0, and the volume fraction of air is 1; each component of velocity and pressure is set to 0; the volume fraction of water in the water area is set to be 1, and the volume fraction of air is 0; both the speed and pressure are set to 0.
(D) And judging whether the flow set by the C meets the convergence requirement or not.
After one-time calculation, the average value alpha of the volume fractions of water on the symmetrical surface of the water area ave1 And =0.75, which indicates that the flow rate is low. The flow rate is adjusted to 0.95/alpha ave1 After =1.26 times, calculate again. The results obtained after the above-described repetition are shown in Table 1.
Table 1 numerical calculation results
As can be seen from table 1, after 3 times of calculation, the flow passing through a single sluice is determined, and the error of the empirical formula is 15.5%, while the error of the CFD-based sluice overflow flow calculation method disclosed by the invention is reduced to 4.2%.
Claims (3)
1. A water gate overflowing flow calculation method based on CFD is characterized by comprising the following steps:
(A) Establishing a geometric model of a sluice calculation domain;
(B) Grid division;
(C) CFD calculation setting; the CFD calculation setting method comprises the following steps:
(1) Importing the grid divided in the step (B) into CFD software ANSYS CFX for setting;
(2) The calculation model and the calculation method are as follows: flow calculation is carried out based on a Reynolds time-mean N-S equation, a standard free surface model is adopted to capture the change of the water surface under a homogeneous flow model, a turbulent flow model adopts a standard k-epsilon model, and each item in the time-mean N-S equation is dispersed by adopting a High Resolution format;
(3) Setting a boundary condition: the water area inlet adopts a flow inlet condition, the volume fraction of water is set to be 1, and the volume fraction of air is set to be; the outlet condition adopts a flow outlet condition, and the flow is estimated according to the following formula:
in the formula, σ s Mu is the coefficient of flooding 0 The flow coefficient of the free outflow of the gate hole, e the opening height of the gate, b the net width of each hole, H 0 The water head is a gate front water head comprising a near flow velocity water head, and g is gravity acceleration; the surface of the middle line in the width direction of the panel is set as a symmetrical surface; the upper surface of the air area adopts an Opening boundary, the pressure is set to be 0, and the volume of water is dividedNumber 0, air volume fraction 1; the interface between the air area and the water area adopts Gerneral Connection; the other boundaries are set as non-slip wall surfaces;
(4) Setting initial conditions: setting the volume fraction of water in an air domain to be 0, and setting the volume fraction of air to be 1; each component of velocity and pressure is set to 0; setting the volume fraction of water in a water area to be 1 and the volume fraction of air to be 0; both the speed and pressure are set to 0;
(D) Judging whether the flow set by the C meets the convergence requirement or not;
the condition for judging whether the flow rate set by the C meets the convergence requirement in the step (D) is as follows:
(1) The average value alpha of the volume fractions of water on the symmetrical surfaces of the water area and the air area ave1 And alpha ave2 As a criterion;
(2) If α is ave1 > 0.95 and alpha ave2 If the flow rate is less than 0.18, the flow rate meets the convergence requirement;
(3) If α is ave1 If the flow rate is less than 0.95, the flow rate is low, and the flow rate is adjusted to the original 0.95/alpha ave1 Doubling;
(4) If α is ave1 > 0.95 and alpha ave2 If the flow rate is more than 0.18, the flow rate is higher, and the flow rate is adjusted to be 0.95/alpha of the original flow rate ave1 And (D) repeating steps (C) and (D) until the convergence requirement is satisfied.
2. The method for calculating the overflowing flow of the water gate based on the CFD, according to claim 1, wherein the method for establishing the geometric model of the computational domain of the water gate in the step (A) is as follows:
(1) According to the geometric parameters of the sluice, three-dimensional modeling software is adopted to establish a three-dimensional geometric model of the sluice;
(2) Taking the position of the gate as a reference, and taking an appropriate value for the distance from the upstream water flow inlet and the downstream outlet to the gate to obtain a three-dimensional model of the flow channel including the water gate, which is a calculation domain of the water;
(3) The water level of the upstream and the downstream are properly extended in the height direction, which is the calculation domain of the air.
3. The method for calculating the overflow flow of the water gate based on the CFD according to the claim 1, wherein the method comprises the following steps: the mesh division method described in step (B) is as follows:
(1) Exporting the calculation domain established in the step (A) to ICEM CFD, and carrying out grid division on the calculation domain;
(2) Setting grid parameters to ensure that the grid is encrypted near a water gate;
(3) Meanwhile, in order to capture the interface between water and air, the grids near the water surface also need to be encrypted;
(4) The total number of grid cells should be controlled to be above a certain number, so as to ensure the reliability of calculation.
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